Preheat the oven to 350℉. Spray three 8-inch cake pans with baking nonstick spray. Line the bottoms with parchment paper circles and spray again. Set aside.
In a medium bowl, sift the flour, baking powder, baking soda, and salt. In a medium saucepan over medium high heat, add sifted cocoa powder, water, and hot cocoa mix. Heat until hot and simmering. Set to side.
2 cups All-purpose flour, 1/4 cup Cornstarch, 2 tsp Baking powder, 1/2 tsp Baking soda, 1 tsp Salt, 1 cup Water, 1 cup Unsweetened cocoa powder, 1/3 cup Hot cocoa mix
In a large bowl, mix oil, sugar, vanilla, eggs, and buttermilk. Add in the chocolate mix and mix. Add the dry ingredients and mix on low speed until combined and no flour lumps remain.
1 cup Oil, 1 3/4 cup White granulated sugar, 1 tsp Pure vanilla extract, 4 Large eggs, 1 cup Buttermilk
Pour the cake batter evenly between the three cake pans. Bake for 20-23 minutes. We want a cake that is ALMOST done baking that needs two more minutes, so a toothpick inserted and you will moist cake on it. Top the two of the cake layers with 10 marshmallows each. Place back in the oven for 2 minutes. Take out the cakes and use your fingers to squish all the marshmallows down.
20 Marshmallows
Let the cakes sit in the hot pans for 10 minutes before transferring to a cooling rack. The marshmallow cakes need to be upright. Cool completely before decorating.